Common sense knowledge means different things to different people. Common sense itself seems to refer to both knowledge and to problem solving and reasoning abilities.
Common sense also relates to everyday knowledge such as knowing how to go to the supermarket and buy a packet of Cornflakes. It relates to everyday reasoning such as how to open the secure top of a new bottle of coke.
However, some things that are common sense to one person, may not seem so to others. For instance, the car mechanic may think that recognising a faulty ignition coil requires only common sense but the medical practitioner may not agree.
Common sense knowledge relates to the things that we need to know simply to function as a full member of our society. It includes, how to greet and talk to others, how to buy provisions, how to travel etc. Other societies may have different common sense knowledge.
For more detail see a discussion of General Knowledge.